Conventional brush structure equipped with spring means for pressing a brush against a commutator is shown in FIGS. 10 and 11. FIG. 10 shows a brush device 21 in which a brush 19 is stored in a holder body 18 fixed to a brush holder 17 and the brush 19 is pressed against an outer-peripheral surface of a commutator 2 by a coil-shape spring 20.
However, in this structure, because most part of side-face portion of the brush 19 is pressed against an inner wall of the holder body 18, a friction force becomes large and smooth sliding of the brush 19 in the longitudinal direction is prevented. As a result, this deteriorates followable function of the brush 19 against the commutator 2, and electric conduction between the commutator 2 and the brush 19 becomes unstable.
A brush device 24 for resolving the above-described problem, shown in FIG. 11, is disclosed in Japanese Patent Laid-Open Publication No. 7-213023. In this device, the brush 19 is formed in substantially arc shape and supported by making part of an outer-peripheral surface of the brush 19 contact an inner wall of a sustaining portion 22.
An outer-peripheral surface of an end portion of the brush 19 at the side of the commutator 2 is made contact the inner wall of the sustaining portion 22 by its friction force with the commutator 2, and an inner-peripheral surface of an end portion of the brush 19 at the side of a torsion spring 23 is made contact the inner wall of the sustaining portion 22 by a pressing force of the torsion spring 23. Accordingly, the brush 19 is supported with a clearance g from the inner wall of the sustaining portion 22, thereby improving followable function of the brush 19 against the commutator 2. Further, forming the brush 19 in arc shape can acquire a wear tolerance of the brush for sliding and also make a size of whole brush device in the radial direction small.
However, the brush device 24 shown in FIG. 11 still has a problem about its secure acquirement of the electric-conduction between the commutator and the brush. In the device shown in FIG. 11, the brush 19 is just supported with the clearance g from the inner wall of the sustaining portion 22, and the commutator 2 of an actual product is constituted of a plurality of commutator pieces 2a. Accordingly, when the brush 19 goes over each of the commutator pieces 2a, supporting of the brush 19 becomes unstable and vibration occurs easily.
Further, in some usages of a motor with a brush, the motor is driven reversely such that the commutator rotates in both clockwise direction and counterclockwise direction. In the brush device shown in FIG. 11, however, the reverse rotation of the commutator 2 in the clockwise direction causes fluttering of the brush 19 due to existence of the clearance g at two portions and supporting of the brush 19 becomes unstable. Accordingly, vibration tends to occur easily.
A brush devise 14 shown in FIGS. 12 and 13 has been materialized as a brush device to resolve the above-described problems. This brush device 14 is constituted such that a plurality of commutator pieces 2a are disposed on an outer-peripheral surface of a motor shaft 1 at regular intervals to form the commutator 2, and a brush 10 made of carbon is inserted in and supported by a supporting shaft 7 at a brush holder 4 that is a stator. The brush 10, as shown in FIG. 12, is constituted of a brush arm portion 10a, which includes a sliding face to provide an electric conduction with contacting the commutator pieces 2a and is formed in arc shape, and a brush base portion 10b, which includes a hole 8 for attaching the brush 10 to the brush holder 4 by inserting the supporting shaft 7 therein. The brush 10 is formed in substantially dogleg shape by integrating the brush arm portion 10a to the brush base portion 10b. Further, pressing means such as a coil-shape spring 5 and the like is provided so as to be coaxial to the supporting shaft 7, so that the sliding surface of the brush 10 contacts and slides on the commutator pieces 2a with pressing thereby.
The brush device 14 can prevent a contacting force of the brush 10 against the commutator 2 from changing due to wearing of the brush 10, by providing pressing means such as the coil-shape spring 5 (only one brush 10 is illustrated), thereby providing excellent stability of the electric conduction between the commutator 2 and the brush 10. Further, it has an advantage that because the brush arm portion 10a, which corresponds to the brush 19 of FIGS. 10 and 11, is supported by a relatively large-sized brush base portion 10b and the brush base portion 10b is inserted to the supporting shaft 7, supporting of the brush becomes stable and any vibration during the motor operation does not occur easily, compared with the brush device of FIGS. 10 and 11.
However, because the conventional device 14 has a structure in which the brush 10 is placed on the coil-shape spring 5 which is pressing means, the thickness of the brush device 14 increases in a direction of the motor shaft 1 accordingly. As a result, there is a problem that the size of the motor with a brush in the direction of motor shaft can not be made small.
The present invention has been devised in view of the above problems, and its object is to provide a brush device in which secure electric conduction between its brush and commutator can be obtained by improving contacting function therebetween, and the thickness thereof in the direction of motor shaft can be made small, compared with the conventional devices.
Further, it is to aim at making the size of a motor with a brush in the direction of a motor shaft small by using the above brush device.